Gail Ruhl and Karen Rane
P&PDL Co-Directors/Senior Plant Disease Diagnosticians

The mission of Purdue's Plant and Pest Diagnostic Laboratory (P&PDL) is to provide accurate and rapid identification of plants, pests, and plant problems; especially those suspected to be of an invasive nature. The lab serves as a source of unbiased information for plant and pest related problems and provides management strategies upon request.

The staff of the Plant and Pest Diagnostic Lab, along with other cooperating Extension Specialists in the Departments of Botany and Plant Pathology, Agronomy, Entomology, and Horticulture diagnosed a total of 3728 problems (Table 1) on samples in 2006 (Table 2).

Of the 1992 sample submissions to the P&PDL, 1899 were submitted as physical samples, 29 were submitted as digital images accompanied by physical samples and 64 were submitted strictly as electronic submissions of digital images to the Lab via a standard web-based method.

Phytophthora ramorum, a regulated plant pathogen, was confirmed for the first time in Indiana on a sample of viburnum collected in July by an IDNR inspector from a retail garden store in Portage, IN. The sample of V. plicatum ‘Mariesii’ was collected as part of a trace forward survey of nursery stock shipped from an Oregon supplier. This is the first time P. ramorum has been detected in Indiana, where surveys as part of the National Phytophthora ramorum Nursery Survey program have been conducted by the Indiana Department of Natural Resources (IDNR) and the Purdue University Plant and Pest Diagnostic Laboratory since 2004. Customers who purchased host plants this spring and summer from the retail store were encouraged, through newspaper articles and the local Cooperative Extension office, to submit symptomatic samples to the Plant and Pest Diagnostic Laboratory for testing. Four additional suspect samples were submitted by homeowners and all tested negative for the presence of any Phytophthora sp. The IDNR press release on this find of P. ramorum in Indiana may be viewed at: http://www.in.gov/serv/presscal?PF=dnr&Clist=11&Elist=86998

Another first time detection for the state of Indiana was the confirmation of Asian Soybean Rust, a plant disease caused by the pathogen, Phakopsora pachyrizae, on a soybean leaf collected October 12, 2006 from double crop soybeans planted at the Purdue South West Ag Center in Knox county. Soybean leaves were collected and submitted upon request following the announcement of the confirmation of SBR in Kentucky. Purdue University Plant and Pest Diagnostic Lab co-directors, Karen Rane and Gail Ruhl, observed a rust pustule on the sample and sent the sample to the National Mycologist USDA-ARS in Beltsville Maryland for positive confirmation and species verification, as indicated by the National protocol for handling of first soybean rust samples in a state. Confirmation of soybean rust was received October 17, 2006. Soybean rust was confirmed on subsequent samples submitted from five additional counties: Pike, Posey, Tippecanoe, Vanderburgh, and Warrick. Soybean harvest was well underway when rust showed up. Even though rains delayed harvest, virtually all of the soybeans in the state were mature, so there was no opportunity for the disease to damage this year’s crop in Indiana.

The majority of routine samples were received by the P&PDL during the months of June, July, and August (Figure 1). Same day service was provided for 6% of the samples received during 2006 and 29% of the samples were completed in three days or less. A total of 51% of the samples received during 2006 were diagnosed within five working days and 78% of all samples received were answered within 10 working days. An extended turn-around time of greater than 10 days (22% of samples) was documented for those samples requiring more extensive culture work and laboratory testing (Figure 2).

Infectious diseases (43%), noninfectious disorders (37%), and arthropod-related problems (13%) were the most common primary diagnoses in 2006 (Figure 3). The most common commodities submitted to the P&PDL were ornamentals (44%) and agronomic crops (33%) (Figure 4). The remaining 23% of samples were distributed among various other commodity groups including turf, vegetables, fruit, specialty crops, and insect, fungal, and aquatic weeds identification. Purdue Extension Specialists and Research Associates provided commodity related summaries of prevalent problems that occurred in 2006.

The Plant and Pest Diagnostic Laboratory (P&PDL) serves as the plant disease diagnostic facility for the Indiana Department of Natural Resources (IDNR) and thus, the P&PDL and IDNR work together during outbreaks of diseases of regulatory concern. In 2006, P&PDL and IDNR staff worked cooperatively to survey nurseries for the presence of Phytophthora ramorum, a disease of regulatory concern. All 801 samples collected from the 20 Indiana nurseries surveyed tested NEGATIVE for the presence of P. ramorum. However, as mentioned above, one trace forward sample collected in Portage, Indiana tested positive for P. ramorum. All remaining host plants at the site were collected and destroyed according to USDA-APHIS-PPQ protocol.

In cooperation with the IDNR, the P&PDL also provided disease diagnosis on 87 corn samples for IDNR's Phytosanitary Certification Program as well as 24 informational diagnoses for field inspectors. A blue mold (Peronospora tabacina) survey was conducted on tobacco samples as a part of the IDNR 2006 Indiana Tobacco Blue Mold Field Survey.